How much a truck can tow is more about weight not length. My 28 RK two slides weighs 11100-11400 depending on how its loaded. My 2500 Dodge/Cummins pulls and handles it with ease.
GM gives your 2500 truck a 6200 rawr that will be carrying all the trailer hitch weight.....hitch in the bed and other gear. The GM 2500 trucks rear axle may weigh in the 3000 lb range leaving around 3200 lb payload in the bed. This equates to a 5th wheel trailer with a 2400-2500 lb or so dry weight.
I doubt your going to find a 10000 lb rv trailer with a 42" length.